1.Field of the Invention
The invention pertains to a waterbed with at least one water-filled mattress, which forms a substantially flat bed surface when in the unloaded state and which is held inside a frame consisting of beams of foamed plastic.
2.Description of the Related Art
Many different designs of waterbeds which have proven to be reliable are known. So-called “soft-side” waterbeds have an upper structure consisting of a dimensionally stable tub, in which one or two separate water-filled mattresses are arranged. A waterbed of this type known from EP 0 240 479 has a mattress which has a shape corresponding to that of the tub-like recess and which is introduced into the one-piece mattress carrier. The recess is concavely curved both in the longitudinal direction and in the transverse direction and is adapted to the outlines of a person lying on the bed in such a way that the concave longitudinal curvature is less pronounced under the leg and foot end and more pronounced under head end. As a result, less water is required to fill the mattress, and thus the weight of the mattress is also reduced. On the mattress, furthermore, a top cover is provided, and immediately below that, lying on the mattress, there is a weight-distribution liner. The top cover, the weight-distribution liner, the mattress, and the mattress carrier are held together by an enveloping sleeve, by means of which the water is also held in the mattress under pressure. When the mattress is now subjected to the additional weight of a person and when, as a result of this load, the top cover and the weight-distribution liner are pushed into the mattress, the water is displaced toward the sides, and a bead is formed along the edges, above the edge of the mattress carrier. This edge area is thus no longer available as a bed surface, because a person lying on the bed will almost always position himself/herself as close to the center as possible because of the shape of the surface caused by the load.
Alternatively, a water-filled mattress can be held by a frame, which usually consists of four individual beams of foamed plastic, which are connected by screws, adhesive, or other types of fastenings to a carrier plate located underneath. The height of the beams is usually the same as the height of the mattress. The beams can be cut to a wide variety of profiles; they can be square or rectangular, for example, as shown in FIG. 1. Alternatively, it is known that these types of square or rectangular beams can be subdivided horizontally and/or vertically as well, as explained, for example, in U.S. Pat. No. 5,228,157, or horizontally according to FIG. 2 as described in DE 101 46 686. By dividing the beam in this way, it is possible to make optimum use of the physical properties of different foamed plastics.
In addition to square or rectangular beams, one-part or multi-part beams which have a bevel on the inside surface are also known. The width of the beam at the top, in cross section, is therefore smaller than that at the bottom, where the beam rests on a carrier plate. There are many different profiles of this type, such as those described in EP 0 240 479, U.S. Pat. Nos. 5,228,157, 4,057,862, and FR 2 669 522, and as illustrated here in FIGS. 3 and 4.
The wedge-shaped beams of foamed plastic which come to a sharp angle at the top where they extend around the mattress have not proven to be acceptable. Although the available bed surface is not reduced around the edges by a frame, a frame of this type lacks sufficient mechanical strength. Under load, e.g., when a person sits on the waterbed, the sharply angled edges of the frame regularly break off.
Because the beams are much stronger and harder than the mattress, a frame of foam beams enclosing the mattress or mattresses thus has the effect of making the available bed surface smaller than the total floor space actually occupied by the waterbed (see FIG. 5). Normally, a “soft-side” waterbed with overall dimensions of 180 cm×200 cm has, on average, a bed surface measuring only about 166 cm×186 cm.